mmg_233_2013_genetics_genomicswikiaorg-20200214-history
AAV1.NT-3 Gene Therapy for Charcot-Marie-Tooth Neuropathies
Charcot-Marie-Tooth Disease (CMT) Charcot-Marie-Tooth disease (CMT) is comprised of a genetically heterogeneous group of sensorimotor peripheral neuropathies. This disease depicts the most frequent inherited disorders affecting the nervous system and is characterized by a progressive loss of muscle tissue and sensory modalities1. A mouse model of the demyelinating form of CMT (CMT1) was used to demonstrate an adeno-associated virus (AAV)-mediated neurotrophin 3 (NT-3) gene therapy trial. CMT1 is the most prevalent inherited neuropathy (prevalence 30/100,000) and CMT1A, a subtype with mutations of peripheral myelin protein 22 (PMP22), represents 70-80% of all known CMTs10. CMT1A arises from a 1.4 Mb duplication at chromosome 17p11.2 (encoding PMP22) and is generally produced as a primary Schwann cell (SC) disease2,3. Although the use of ambulatory aids is common, this condition is without treatment for bilateral foot drop, symmetric muscle atrophy below the knee, weakness of hands10 and/or onset between 5 and 25 years4,5. Neurotrophin 3 (NT-3) NT-3, expressed by SCs, is involved in an autocrine survival loop allowing SCs to survive and differentiate in the absence of an axon via neurite outgrowth stimulation and myelination6,7. It was hypothesized that priming SCs with NT-3 could lead to axonal regeneration and corresponding myelination, thus providing a critical first step in CMT neuropathy treatment8. This was further proven in studies on the tremblerJ (TrJ) mouse, an animal model with naturally occurring CMT due to a point mutation in the PMP22 gene, in which subcutaneous injections greatly improved axonal regeneration and enhanced myelination 9. For these reasons, among others, NT-3 is considered for potential in gene thereapy for CMT1A. The short serum half-life and need for repeated doses of NT-3, however, led to the consideration of AAV-mediated gene delivery in which the AAV1 vector carrying NT-3 provides a continuous source of NT-3 serum levels within skeletal muscle10. Gene Therapy An AAV expression cassette containing the human NT-3 cDNA under control of a triple muscle creatine kinase (tMCK) promoter11 was packaged in self-complimentary (sc) AAV1 vectors. A dose response study was then performed at differing time intervals to study and compare serum NT-3 levels following injection of scAAV1.tMCK.NT-3 at 3 doses (3x109 vg, 1x1010 vg and 3x1010 vg). It was observed that a dose of 3x1010 vg showed functional efficacy in achieving sustained NT-3 levels. This gene transfer into muscle tissue resulted in NT-3 secretion into circulation (reaching therapeutic blood levels) that was sufficient to provide functional, histopathological and electrophysiological improvements in peripheral nerves10. Adverse Effects Although no direct adverse effects have been observed due to an increase in AAV expressed NT-3 levels, increased levels in the neurotrophin family in general have been shown to induce changes within the ventral tegmental area (VTA) in rats. Specifically, increased neurotrophin levels have been noted to induce an opiate-dependent like reward state when injected directly into the VTA (i.e. the animals began to act as if they were dependent on opiates)12. Although not directly associated with an increase in circulating NT-3 levels, this induction of an opiate-dependent like reward state could potentially result from the described gene therapy and should thus be considered when administering treatment. References # Skre H. Genetic and clinical aspects of Charcot-Marie-Tooth’s disease. Clinical Genetics. 6':98-118 (1974). #Lupski JR. DNA duplication associated with Charcot-Marie-Tooth disease. '' Cell. '''66:219-232 (1991). #Raeymaekers P, et al. Duplication in chromosome 17p11.2 in Charcot-Marie-Tooth neuropathy type 1a (CMT 1a). Neuromuscular Disorders. 1':93-97 (1991). #Marques W Jr., ''et al. 17p duplicated Charcot-Marie-Tooth 1A : characteristics of a new population. Journal of Neurology. '''252:972-979 (2005). #Houlden H, Reilly MM. Molecular genetics of autosomal-dominant demyelinating Charcot-Marie-Tooth disease. Neuromolecular Medicine. 8':43-62 (2006). #Frostick SP, Yin Q, Kemp GJ. Schwann cells, neurotrophic factors, and peripheral nerve regeneration. ''Microsurgery. '''18:397-405 (1998). #McTigue DM, Horner PJ, Stokes BT, Gage FH. Neurotrophin-3 and brain-derived neurotrophic factor induce oligodendrocyte proliferation and myelination of regenerating axons in the contused adult rat spinal cord. J Neuroscience. 18:5354-5365 (1998). #Sahenk Z. Neurotrophins and peripheral neuropathis. Brain pathology. 16:311-319 (2006). #Sahenk Z, et al. NT-3 promotes nerve regeneration and sensory improvement in CMT1A mouse models and in patients. Neurology. 66:681-689 (2005). #Sahenk Z, Galoway G, Clark KR, Malik V, Rodino-Klapac LR, Kaspar B, Chen L, Braganza C, Montgomery C, Mendell JR. AAV1.NT-3 gene therapy for Charcot-Marie-Tooth neuropathy. Molecular Therapy accepted article preview online (2013); doi:10.1038/mt.2013.250. #Wang B, et al. Construction and analysis of compact muscle-specific promoters for AAV vectors. Gene Therapy. 15:1489-1499 (2008). #Vargas-Perez H, Ting-A KR, Walton CH, Hansen DM, Razavi R, Clarke L, Bufalino MR, Allison DW, Steffensen SC, van der Kooy D. Ventral tegmental area BDNF induces an opiate-dependent-like reward state in naive rats. Science. '324 '(5935):1732-1734 (2009).